Field of the Invention
The present invention relates generally to the field of wireless communication. In particular, the present invention relates to Specific Absorption Rate (SAR) reduction techniques and related antenna systems that preserve communication link performance while managing near-field radiation characteristics of antenna systems.
Related Art
Today's mobile wireless devices must meet a stringent set of requirements that relate to the radiated performance of the antenna system on the mobile side. These requirements cover parameters such as total radiated power (TRP), total isotropic sensitivity (TIS), specific absorption rate (SAR), and hearing aid compatibility (HAC). SAR tends to increase with increasing TRP, as well as interference which will cause HAC to fail to meet requirements. One method to reduce SAR in a wireless mobile device is to reduce the transmit power. This technique, unfortunately, results in reduced communication link quality caused by decreased transmit power.
Proximity sensors and other sensing devices are being integrated into current cell phones and other mobile wireless devices. This is typically done to serve such functions as powering down the display when the cell phone is placed against the user's head. This results in power savings which translates into increased battery life, an important parameter in mobile wireless devices. Another function enabled by proximity sensors is the reduction of transmit power of Tablet PCs when hand or body loading is sensed, which results in reduced SAR at the expense of radiated efficiency.
Commonly owned U.S. Pat. No. 7,911,402, issued Mar. 22, 2011, describes a Modal antenna capable of dynamically shifting frequency response and radiation pattern characteristics of the modal antenna; the entire contents of which are hereby incorporated by reference.
Commonly owned US pub. 2014/0099982, published Apr. 10, 2014, describes a modal adaptive antenna system, which uses an antenna radiation pattern beam steering technique to improve communication link quality between the mobile wireless device and the base terminal. This technique provides an antenna with multiple radiation pattern states, or modes, along with an algorithm to dynamically sample link performance and adjust the radiation pattern of the mobile antenna to improve communication link quality. This technique is designed to improve the communication link quality, which is a far-field parameter.
Commonly owned US pub. 2013/0127670, published May 23, 2013, describes a technique of dynamically sampling near-field properties derived from proximity sensors or other sensors integrated into a mobile device and use this information to modify the antenna radiation pattern of a modal antenna to improve communication link quality along with near-field parameters such as SAR. An algorithm and look-up table containing pre-measured electrical parameters to include TRP, TIS, and SAR are developed and integrated with hardware which includes an antenna and active components to dynamically modify the radiation pattern of the antenna as well as proximity sensors and or other sensing devices.